Stardust's Data May Be Contaminated, Report Says

The origin of the universe has been the subject of science—and science fiction—for centuries. NASA's Stardust Mission, launched in 1994, aimed to put an end to the pondering once and for all by collecting samples from Comet Wild-2, which scientists believed might still contain materials from the universe's conception (and which recently brought more details about the diversity of comets themselves). When the mission finally returned to Earth last year (and we tracked its landing from the air), the samples revealed the presence of osbornite, which indicates that the big beginning was hotter and more violent than scientists had previously imagined.

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But a new report insists there may be another reason for the presence of the mineral in Stardust's samples: Contamination by rocket fuel, which contains Titanium Nitride— osbornite's chemical compound.

"The [Stardust theory] is a perfectly plausible [one]," says the report, from Spanish astrobiologists and set to appear in the May 16th issue of Energy & Fuels. "Nevertheless, we believe it necessary to call attention to the existence of other… possibilities to form titanium nitride that have not been considered."

The report concedes that "careful measures were taken" to control and prevent contamination. Donald Brownlee, principle investigator on the Stardust Project and professor at the University of Washington, believes these measures were so robust that contamination from rocket fuel isn't likely—and that the mineral's composition confirms this rebuke of the new report.

"It's always a concern," Brownlee says, "but I'm confident that the titanium nitride we see in the Stardust particles is not a contaminant. It's encased inside a variety of solid mineral grains; it couldn't have come from the outside. That's like saying the inside of a diamond came from your car exhaust." Brownlee also notes that a contaminant would have been more prevalent than what was found on Stardust, which has only tiny components of osbornite in two samples.

To capture particles from the comet, Stardust extended tennis racket-shaped screens of silica aerogel. The particles burrowed into the gel at high speed, leaving carrot-shaped tracks. "The good thing about that," says Brownlee, "is that if anything else had come in after it, we would be able to see it. And there's no evidence of that." According to Brownlee, Stardust scientists haven't found any possible contaminents associated with captured particles other than aerogel.

Regardless, the Stardust Mission would be significant even if the presence of titanium nitrade was a result of contamination; after all, it was the first spacecraft to bring home intact comet and interstellar dust samples, a feat that earned the mission a 2006 Popular Mechanics Breakthrough Award. "We're still finding really great stuff from it," says Brownlee. "The plan is to not consume all the samples; they're long-term resources. We still want to be studying them a decade or more from now. We might not get another comet sample for awhile." —Erin McCarthy